This invention relates to an electronic clinical thermometer and, more particularly, to an electronic clinical thermometer which, when brought into contact with the surface of a living body, senses that the instrument is in a state enabling the body temperature to be measured.
With the rapid progress that has been made in semiconductor technology, electronic clinical thermometers have become available in which a microcomputer, namely a computer mounted on a single chip, is accommodated in an enclosure of approximately the same size as the conventional glass clinical thermometer. The electronic clinical thermometer of this type measures and displays body temperature using a battery such as a mercury lithium cell as the power supply. Owing to the large power consumption of the microcomputer, however, compact electronic clinical thermometers that rely upon batteries of a small capacity are attended by such problems as the comparatively short interval between battery changes and the likelihood of reading errors caused by run-down batteries. Some conventional electronic clinical thermometers are provided with a manually operable power switch, while others are so designed that the power supply turns on only when a measurement is actually performd. Electronic clinical thermometers of this latter type employ a touch switch or pressure switch in order to eliminate the manual switch operation, or use the touch or pressure switch in combination with a manual switch in order to reduce power consumption by interrupting the flow of current expended in measurement whenever the thermometer is not actually in contact with the body.
In the touch switch arrangement, it is common practice to use a sensing element, namely a variable impedance element, such as a capacitor or coil, of the type which experiences a change in impedance when brought close to or in contact with the human body. Since the thermometer is used with a sheath covering the probe associated with the sensing element, however, the effect of such an arrangement is a marked decline in reliability.
In another aspect, an electronic clinical thermometer equipped with a high-impedance contact sensor is adapted to sense the start of measurement by bringing the sensor into contact with the human body. However, owing to such factors as a variance in the thickness of the sheath, a variance in the gap between the sheath and the contact sensor as well as between the sheath and body surface, both reactance-variable and impedance-variable sensors fail to develop a sufficient change in impedance. Moreover, the sheath itself is electrically insulated. A sensor configuration of the above type therefore does not always guarantee that contact with the human body will be sensed with a high degree of reliability. Furthermore, touch or contact switches do not necessarily reduce power consumption to a satisfactory extent, so that the problem of rapid battery consumption remains.